Calcium silicate insulating material containing alumina silica microspheres

ABSTRACT

An asbestos free, calcium silicate insulating material suitable for use in the casting of molten non-ferrous metals, and suitable for use in applications where a fire resistant, heat insulating, electrical insulating, and corrosion resistant material is desirable. The calcium silicate insulating material is produced by combining lime, a siliceous component, alumina silica microspheres, wollastonite and organic fibrous material in the presence of water to form a slurry. The slurry is then placed under steam pressure, to react the lime, siliceous component and water, dried, and heat treated if necessary.

FIELD OF THE INVENTION

[0001] The present invention relates generally to improved insulatingheat-resistant materials containing alumina silica microspheres andmethods of producing such materials. The present invention furtherrelates to such materials containing alumina silica microspheres andmethods wherein the resulting materials produced are suitable for use inthe casting of non-ferrous metals such as aluminum and similar metals.

BACKGROUND OF THE INVENTION

[0002] A variety of insulating heat-resistant materials suitable for usein casting of non-ferrous metals are well known in the prior art. Of theinsulating heat-resistant materials utilized in the process of castingnon-ferrous metals that are known in the prior art, calcium silicatebased materials have proven to be of particular utility because of theirsmall heat capacities, high heat insulating capability and non-wettingproperties in contact with molten non-ferrous metals.

[0003] Calcium silicate based insulating materials employed in castingof non-ferrous metals have typically been of the tobermorite-type matrixstructure and xonotlite-type matrix structure of calcium silicateinsulating material.

[0004] A fundamental tobermorite-type matrix structure of calciumsilicate insulating material is disclosed in U.S. Pat. Nos. 4,111,712and 4,128,434 to Pusch. This fundamental tobermorite type matrixstructure of calcium silicate insulating material is produced bycombining a source of calcium, such as hydrated lime or quick lime, asource of siliceous material, such as silica, diatomaceous earth, silicafume, colloidal silica, or other suitable oxides of silicon, fibrouswollastonite and an organic fiber, such as kraft made from wood pulp, inthe presence of water to form an aqueous slurry. The aqueous slurry isthen poured into a mold where the excess water is pressed out of themixture to form an uncured shape, typically a sheet. The uncured shapeis then placed in an autoclave where it is heated under steam pressureof about 100 psi. The shape is then oven dried to about 250 degreesFahrenheit, and subsequently heat treated to above 500 degreesFahrenheit. Finally, the resultant tobermorite type calcium silicateinsulating material is cut or machined to the appropriate dimensions foruse in the particular application.

[0005] As with the tobermorite-type matrix structure of calcium silicateinsulating material, the xonotlite-type matrix structure of calciumsilicate insulating material is known in the prior art. A fundamentalxonotlite-type matrix structure of calcium silicate insulating materialis produced by mixing a source of calcium, such as hydrated lime orquick lime, a source of siliceous material, such as silica, diatomaceousearth, silica fume, colloidal silica, or other suitable oxides ofsilicon, fibrous wollastonite, an organic fiber, such as kraft made fromwood pulp and water in an autoclave under about 200 psi steam pressure.The resultant aqueous slurry is then pressed in a mold and dried in anoven.

[0006] Alternatively, the fundamental xonotlite-type matrix structure ofcalcium silicate insulating material may be produced by mixing a sourceof calcium, such as hydrated lime or quick lime, a source of siliceousmaterial, such as silica, diatomaceous earth, silica fume, colloidalsilica, or other suitable oxides of silicon, fibrous wollastonite, anorganic fiber, such as kraft made from wood pulp in the presence ofwater to form an aqueous slurry. The aqueous slurry is then poured intoa mold where the excess water is pressed out of the slurry to form anuncured shape, typically a sheet. The uncured shape is then placed in anautoclave where it is heated under steam pressure of about 200 psi. Theshape is then oven dried.

[0007] Finally, the resultant xonotlite type calcium silicate insulatingmaterial is cut or machined to the appropriate dimensions for use in theparticular application.

[0008] Although these fundamental tobermorite type and xonotlite typecalcium silicate insulating materials have been found to be suitable foruse in connection with the casting of relatively low melting pointnon-ferrous metals and in other uses, certain shortcomings of theseinsulating materials have become apparent in application. In producingan optimal calcium silicate insulating material, it is desirable thatthe insulating material have reduced density, increased strength,improved thermal insulating properties, be homogeneous throughout withminimized thermal shrinkage. Of particular importance for calciumsilicate insulating material utilized in connection with the casting ofnon-ferrous metals, such as aluminum, is the necessity that the materialhave sufficient physical strength. In casting non-ferrous metals, suchas aluminum, the insulating material that comes in contact with theelevated temperature of the molten metal is particularly susceptible tocracking and fracture; therefore sufficient physical strength andthermal dimensional stability are required of the insulating material.Additionally, in connection with the casting of non-ferrous metals, itis desirable that outgassing of the insulating material in contact withthe molten metal be minimized. Several variants and improvements of thetobermorite type and xonotlite type calcium silicate insulatingmaterials are known in the prior art which attempt to rectify theshortcomings of the fundamental tobermorite type and xonotlite typecalcium silicate insulating materials.

[0009] In the past, asbestos fibers had been utilized as a reinforcingfiber in manufacture of calcium silicate insulating materials to providesufficient strength and toughness to the insulating material. Althoughsuch asbestos containing insulating materials performed well, the use ofasbestos fibers has been widely discontinued due to health andenvironmental concerns.

[0010] U.S. Pat. No. 5,073,199 to Krowl et al. discloses a tobermoritetype calcium silicate insulating material containing pitch basedgraphite fiber to provide toughness and strength to the insulatingmaterial. However, the incorporation of such graphite fiber and itsassociated material cost results in an appreciable increase in the costof the resultant product.

[0011] U.S. Pat. No. 4,690,867 to Yamamoto et al. discloses a xonotlitetype calcium silicate insulating material with improved strengthsuitable for non-ferrous metal casting wherein reinforcing carbon fibersare not uniformly distributed in the material thus having zones ofvarying strength. Use of the material disclosed in U.S. Pat. No.4,690,867 for molten metal casting is often accompanied by undesirableoutgassing which creates voids and contaminants in the resultant castmetal.

[0012] U.S. Pat. Nos. 4,773,470 and 4,897,294 to Libby, et al. disclosethe use of delaminated vermiculite as a substitute for asbestos in thecomposition of a tobermorite insulating material suitable for use inmolten metal casting. Although the use of vermiculite as a substitutefor asbestos results in material with reduced thermal shrinkage incomparison to materials containing only wollastonite as the inorganicfiber, the machineability of the material is compromised.

[0013] As a final example of attempts of the prior art to rectify theshortcomings of the fundamental tobermorite type and xonotlite typecalcium silicate insulating materials, U.S. Pat. No. 4,144,121 toOtouma, et al. and U.S. Pat. No. 4,334,931 to Assumi, et al. disclosethe use of previously synthesized xonotlite crystalline material toprovide strength comparable to that of an asbestos containing board.However, manufacture of these calcium silicate insulating materials ismore costly, in that, an additional step is required to produce thexonotlite crystalline material that is incorporated with the startingmaterials.

[0014] Accordingly, it is the principle objective of the presentinvention to provide an insulating material that is suitable for use innon-ferrous molten metal casting that is lightweight with greaterrefractoriness, is tough and resistant to high temperature cracking, anddoes not possess the shortcomings of the prior art insulating materials.

[0015] An additional objective of the present invention is to provide anasbestos-free fire resistant, heat insulating, electrical insulating,and corrosion resistant material, that may be utilized in otherapplications in addition to non-ferrous metal casting, having reducedhealth exposure risk and minimal environmental impact.

[0016] Other objects and advantages of the present invention will beapparent to those skilled in the art from the following description ofthe invention.

SUMMARY OF THE INVENTION

[0017] The present invention is an asbestos-free thermal insulatingmaterial that is resistant to high temperature cracking that is formedfrom a mixture consisting essentially of, in parts by weight percentage:12 to 40 weight percent of lime, 12 to 40 weight percent of a siliceouscomponent, 0 to 70 weight percent of wollastonite, up to 70 weightpercent of alumina silica microspheres, and 0 to 10 weight percent oforganic fiber, in the presence of water to form a aqueous slurry;molding the aqueous slurry into a shape and expelling excess water;curing the molded shape under appropriate steam pressure for sufficienttime to cause the lime siliceous component and water to react to formthe desired tobermorite or xonotlite hydrated calcium silicate matrixreinforced by the alumina silica microspheres and wollastonite, ifpresent; thereafter, the cured shape is dried, heat treated and machinedto particular shape, if desired.

[0018] Should a pre-mold reacted process be employed to form xonotlite,the above mixture, in the presence of water, is reacted underappropriate steam pressure for sufficient time to cause the lime,siliceous component and water to react to form the desired xonotlitehydrated calcium silicate matrix; molding the slurry into a shape andexpelling excess water; thereafter, the molded shape is dried andmachined to particular shape, if desired.

DETAILED DESCRIPTION OF THE INVENTION AND PREFERRED EMBODIMENTS

[0019] The principal components of the present invention are a calciumsource, a siliceous component, alumina silica microspheres,wollastonite, if desired, and a small amount of organic fiber, ifdesired.

[0020] The calcium source may be any suitable hydrated lime or quicklime. The amount of lime utilized by weight is from 12 to 40 percent,and preferably from 14 to 20 percent, of the total weight of thecomponents other than water.

[0021] The siliceous component utilized may be of any substantially puresources of silica such as silica, diatomaceous earth, silica fume,colloidal silica, or other suitable oxides of silicon. The amount ofsiliceous component utilized by weight is from 12 to 40 percent, andpreferably from 14 to 20 percent, of the total weight of the componentsother than water. The lime and siliceous component are utilized in aratio suitable for the desired formation of the tobermorite or xonotlitehydrated calcium silicate matrix that forms through the reaction of thelime, siliceous component and water under appropriate conditions.

[0022] The alumina silica microspheres are lightweight hollow sphericalparticles, extracted from pulverized fuel ash generated by coal firedfurnaces, such as those utilized in coal fired power stations, and arecomposed primarily of silica and alumina as their major components withsome iron oxides as a minor component. The melting point of the aluminasilica microspheres is above 2100 degrees Fahrenheit. As the aluminasilica microspheres possess such a high melting point, they areparticularly suitable for use in the calcium silicate based insulatingmaterial of the present invention and its applications includingnon-ferrous metal casting. Additionally, as the microspheres are hollow,the density of the resultant insulating material of the presentinvention is reduced and its refractoriness is increased. Further, asthe shells of the microspheres are remarkably strong, they are able toeasily withstand the rigorous mixing, pressing and treatment involved inthe process of manufacturing the reacted calcium silicate insulatingmaterial of the present invention.

[0023] Suitable microspheres for use in the present invention areavailable, from the PQ Corporation under the trademark EXTENDOSPHERESand from Trelleborg Fillite, Inc. under the trademark FILLITE, withvarious grades and sizes. The present invention is not criticallysensitive to the alumina and silica content of the various grades ofmicrospheres; the alumina content of the various currently availablegrades of microspheres range from 27 to more than 43 weight percent, andthe silica content ranges from 55 to 65 weight percent of themicrospheres total weight. The size of the microspheres is also notcritical to the present invention; microspheres are currently availablein the range of about 5 to about 500 microns in size, all of which aresuitable. A particularly suitable microsphere, because of its relativelylow cost, is EXTENDOSPHERES SG which is composed of 58 to 65 weightpercent silica, 28 to 33 weight percent alumina, and up to 4 weightpercent iron oxides, with a mean particle diameter of 120 to 130microns. The amount of silica alumina microspheres utilized by weight isup to 70 percent, and preferably from 10 to 30 percent, of the totalweight of the components other than water.

[0024] Wollastonite is a crystalline form of anhydrous calcium silicate.In the present invention, the wollastonite, if used, preferably has aparticle size whereby 60 weight percent of its particles pass through asieve no. 50 mesh screen. The wollastonite, if used, is up to 70percent, and preferably from 30 to 50 percent, of the total weight ofthe components other than water.

[0025] An organic fiber may be incorporated to facilitate the handlingand molding of the insulating material of the present invention and toprovide green strength in the process of manufacture. The amount oforganic fiber utilized is up to 10 percent, and preferably from 4 to 8percent, of the total weight of the components other than water. Theorganic fiber may be wood fiber, polyester or other synthetic fiber,cotton or other natural fibers. Kraft, which is made from wood pulp isparticularly preferred.

[0026] To form a calcium silicate insulating material of the presentinvention containing a predominantly and substantially pure tobermoritetype hydrated calcium silicate matrix, the lime, the siliceous material,the alumina silica microspheres, the wollastonite, if utilized, and theorganic fiber, if utilized, are mixed in the presence of water to forman aqueous slurry. Mixing occurs with such vigor and for such time as isnecessary to thoroughly disperse the dry solid materials throughout theslurry. The aqueous slurry is then placed into a mold where excess wateris pressed from the aqueous slurry to form a shape retaining moldedbody. A typical shape of the molded body is a flat 4 foot by 8 footsheet about ½ to 4 inches thick. The molded body is then cured underhigh pressure steam for such time and at such pressure as necessarycause the lime, siliceous material and water to react to form thetobermorite calcium silicate hydrate crystalline matrix. Steam pressureof about 100 psi for a period of about 24 to 32 hours has been employedto form a satisfactory tobermorite crystalline matrix; however othervariations of time and steam pressure which are known in the art may beemployed.

[0027] The cured body may then be oven dried to about 250 degreesFahrenheit to reduce its moisture content and subsequently heat treatedto burn away any organic fiber material that was utilized to facilitatehandling and molding and provide green strength for the manufacturingprocess.

[0028] To form a calcium silicate insulating material of the presentinvention containing a predominantly and substantially pure xonotlitetype hydrated calcium silicate matrix, the above steps for forming theinsulating material having a tobermorite type hydrated calcium silicatematrix are followed with the exception that the heat treatment step iseliminated and the molded body is cured under high pressure steam forsuch time and at such pressure as necessary to cause the lime, siliceousmaterial and water to react to form the xonotlite calcium silicatehydrate crystalline matrix. Steam pressure of about 200 psi for a periodof about 15 to 20 hours has been employed to form a satisfactoryxonotlite crystalline matrix; however other variations of time and steampressure which are known in the art may be employed.

[0029] Additionally, a calcium silicate insulating material of thepresent invention containing a predominantly and substantially purexonotlite type hydrated calcium silicate matrix may be manufactured byan alternate method. In this alternate method, the lime, the siliceousmaterial, the alumina silica microspheres, the wollastonite, ifutilized, and the organic fiber, if utilized, are mixed to form a slurryunder high pressure steam for such time and at such pressure asnecessary to cause the lime, siliceous material and water to react toform xonotlite. Thereafter, the reacted aqueous slurry is placed into amold where excess water is pressed from the aqueous slurry to form amolded body. The molded body may then be oven dried.

[0030] Some of the beneficial properties of the insulating material ofthe present invention are illustrated by way of the followingnon-limiting comparative examples. In each of the following examples,insulating materials of particular component formulations cured to atobermorite type hydrated calcium silicate crystalline matrix wereprepared as follows:

[0031] The components were mixed in the presence of water to form anaqueous slurry.

[0032] The aqueous slurry was then transferred into a mold and pressedto 700 psi, where the excess water was pressed from the aqueous slurryto form a green state flat sheet with the dimensions of 3 inches by 8inches in comparative example 1, and 4 feet by 8 feet sheet incomparative examples 2 and 3. To ensure validity of comparison, testsamples within each comparative example were pressed within the samemold and press.

[0033] The molded sheet was then cured under steam pressure of 100 psifor 24 hours causing the lime, siliceous material and water to react toform the tobermorite calcium silicate hydrate crystalline matrix.

[0034] The cured sheet was then oven dried to 250 degrees Fahrenheituntil it reached an equilibrium moisture constant.

[0035] Finally the sheet was heat treated to above 500 degreesFahrenheit, thereby burning away the organic fiber, until the mass ofthe sheet reached equilibrium.

COMPARATIVE EXAMPLE 1

[0036] The following table sets forth the formulation variables incontent of wollastonite and alumina silica microspheres of seven testsamples and their measured density, modulus of rupture (bendingstrength) and calculated strength factor. The test samples were preparedwith a formulation expressed in weight percent of the total components,other than water, of 17 percent hydrated lime, 17 percent silica flour,6 percent kraft and the remainder as alumina silica microspheres andwollastonite, with the microsphere content increasing in 10 percentincrements, as indicated in the table.

[0037] An important performance criterion for calcium silicateinsulating material utilized in the casting of non-ferrous metals is itsmodulus of rupture (bending strength). Consistently, a higher densitymaterial will yield a higher modulus of rupture. To properly evaluatethe strength characteristics of materials with different densities, aformula is employed to normalize the impact of variation in density; astrength factor, which normalizes this variation and allows comparisonsto be made, is equal to the modulus of rupture (bending strength)divided by the density squared. COMPARATIVE EXAMPLE 1 TABLE test samplenumber 1 2 3 4 5 6 7 microspheres (in weight percent) 0 10 20 30 40 5060 wollastonite (in weight percent) 60 50 40 30 20 10 0 density (inlbs/ft³) 65.0 52.1 47.6 44.1 42.5 38.1 36.8 modulus of rupture (bending1400 1067 1155 794 856 639 468 strength in psi) strength factor (MOR/D²).33 .39 .51 .41 .47 .44 .35

[0038] observed from test sample 1, which contains no microspheres, andtest sample 3, which substitutes 20 percent weight of microspheres for acorresponding amount of wollastonite, that the strength factor, which isnormalized for variations in density, can be increased by thesubstitution of microspheres for wollastonite, while at the same timeoverall density is reduced. Further, it becomes apparent from the testsample results, and in particular the results of test sample 7, in whichall of the wollastonite has been replaced by microspheres, that themicrospheres in the present invention are bound to or are being tightlyincorporated with the calcium silicate matrix. Typically, when densityis reduced by incorporation of low density insulating materials, such asperlite and vermiculite, the strength of the material is reduceddramatically.

COMPARATIVE EXAMPLE 2

[0039] In this comparative example, a calcium silicate material testsample of the prior art, not containing alumina silica microspheres, wascompared to a similar test sample formulation of the present inventioncontaining alumina silica microspheres. Both test samples were preparedwith a formulation expressed in weight percent of the total components,other than water, of 17 percent hydrated lime, 17 percent silica flour,and 6 percent kraft. In the test sample of the prior art material, theremaining 60 percent component was composed of wollastonite; and in thetest sample formulation of the present invention the remaining portionwas composed of 20 percent alumina silica microspheres and 40 percentwollastonite.

[0040] Three specimens from both samples were cut to dimensions of 1inch by 1 inch by 12 inches. The specimens were then conditioned at 250degrees Fahrenheit for 24 hours to normalize the specimens and removeany moisture they may have accumulated. One specimen at a time wassubmerged in a liquid aluminum bath of a known alloy at a temperature of1350 degrees Fahrenheit so that the wetted end of the specimen was threeinches below the surface of the aluminum. The outgassing from thespecimen was observed as bubbles from the liquid aluminum. The durationthat the bubbles were observed, from the time of contact with the liquidaluminum to the cessation of the bubbles was recorded along with thesize of the bubbles observed.

[0041] Calcium silicate insulating materials, even when heat treated,exhibit some amount of out gassing when exposed to liquid non-ferrousmetals. This outgassing, or bubbling in the molten metal, is caused bythe expansion of the air that exists in the calcium silicate insulatingmaterial as it is taken from room temperature and exposed to moltenmetal. Minimization of outgassing is desirable to prevent contaminationof the cast metal and prevent injury from molten metal. The amount ofoutgassing from a calcium silicate insulating material can be evaluatedby observing the duration and size of bubbles exhibited when the calciumsilicate insulating material is immersed in molten metal, wherein it ispreferable to observe smaller bubbles and shorter duration.

[0042] The specimens from the test sample of the prior art were observedto exhibit outgassing effects of about 3 minutes duration with mediumsized bubbles, whereas the specimens of a formulation of the presentinvention were observed to exhibit outgassing effects for only about 2minutes duration with medium sized bubbles.

COMPARATIVE EXAMPLE 3

[0043] In this comparative example, a calcium silicate material testsample of the prior art, not containing alumina silica microspheres, wascompared to a similar test sample formulation of the present inventioncontaining alumina silica microspheres. Both test samples were preparedwith a formulation expressed in weight percent of the total components,other than water, of 17 percent hydrated lime, 17 percent silica flour,and 6 percent kraft. In the test sample of the prior art material, theremaining 60 percent component was composed of wollastonite; and in thetest sample formulation of the present invention the remaining portionwas composed of 20 percent alumina silica microspheres and 40 percentwollastonite.

[0044] The 4 foot by 8 foot sheet test samples were then cut into 32 1foot by 1 foot square specimens. The specimens were each weighed andmeasured in length, width, and thickness to calculate the density inpounds per cubic foot of each specimen. Thereafter the maximum variationwithin each test sample was calculated.

[0045] It is desirable that calcium silicate insulating materials beuniform and consistent throughout. Consistency and uniformity of theinsulating material increases its thermal shock resistance, resulting ingreater crack resistance when placed in contact with molten metal.Additionally, consistency and uniformity of the insulating materialfacilitates machining, and ensures consistent density of parts machinedfrom a sheet of insulating material, irrespective of the origin locationof the pre-machined blank within the sheet of the insulating material.

[0046] The maximum and minimum density measured from specimens of theprior art test sample were 78.5 lbs/ft³ and 62.0 lbs/ft³ respectively.The prior art test sample therefore exhibited a measured variation indensity within the 4 foot by 8 foot sheet of 16.5 lbs/ft³. In comparisonthe maximum and minimum density measured from the specimens of thepresent invention test sample were 52.3 lbs/ft³ and 48.0 lbs/ft³ Thepresent invention test sample therefore exhibited a measured variationin density within the 4 foot by 8 foot sheet of only 4.3 lbs/ft³, adramatic increase in uniformity and consistency.

What is claimed is:
 1. A calcium silicate insulating material formedfrom a mixture, in the presence of water, comprising: 12 to 40 weightpercent lime, 12 to 40 weight percent of siliceous component and up to70 weight percent alumina silica microspheres.
 2. A calcium silicateinsulation material as in claim 1, wherein said mixture furthercomprises up to 10 weight percent organic fiber.
 3. A calcium silicateinsulation material as in claim 1, wherein said mixture furthercomprises up to 70 weight percent wollastonite.
 4. A calcium silicateinsulation material as in claim 2, wherein said mixture furthercomprises up to 70 weight percent wollastonite.
 5. A calcium silicateinsulating material as in claim 2, wherein the amount of said lime ofsaid mixture is 14 to 20 weight percent, the amount of said siliceouscomponent of said mixture is 14 to 20 weight percent, the amount of saidalumina silica microspheres of said mixture is 52 to 68 weight percent,and the amount of said organic fiber is 4 to 8 weight percent .
 6. Acalcium silicate insulating material as in claim 4, wherein the amountof said lime of said mixture is 14 to 20 weight percent, the amount ofsaid siliceous component of said mixture is 14 to 20 weight percent, theamount of said alumina silica microspheres of said mixture is 10 to 30weight percent, the amount of said wollastonite is 30 to 50 weightpercent and the amount of said organic fiber is 4 to 8 weight percent.7. An insulating material as in claims 1 through 6, wherein said limeand said siliceous component have reacted to form a predominantlytobermorite phase calcium silicate hydrate matrix.
 8. An insulatingmaterial as in claims 1 through 6, wherein said lime and said siliceouscomponent have reacted to form a predominantly xonotlite phase calciumsilicate hydrate matrix.
 9. A method for producing a calcium silicatetype insulating material, including the steps of: a. molding a shapefrom an aqueous slurry of a mixture comprising: 12 to 40 weight percentlime, 12 to 40 weight percent siliceous component, up to 70 weightpercent alumina silica microspheres, 0 to 70 weight percentwollastonite, and 0 to 10 weight percent organic fiber; b. curing saidshape in an atmosphere of steam at sufficiently elevated pressure forsufficient time to cause the lime, siliceous component, and water toform a calcium silicate hydrate matrix. c. drying said shape to removeexcess water.
 10. A method for producing a calcium silicate typeinsulating material as in claim 9, wherein the amount of said lime ofsaid mixture is 14 to 20 weight percent, the amount of said siliceouscomponent of said mixture is 14 to 20 weight percent, the amount of saidalumina silica microspheres of said mixture is 10 to 30 weight percent,the amount of said wollastonite of said mixture is 30 to 50 weightpercent, and the amount of said organic fiber of said mixture is 4 to 8weight percent.
 11. A method for producing a calcium silicate typeinsulating material as in claim 10, further comprising the step of heattreating said shape to above 500 degrees Fahrenheit.
 12. A method forproducing a calcium silicate type insulating material as in claim 10,wherein the amount of said pressure utilized and the duration of saidtime employed in the curing step (b) result in a predominantlytobermorite phase of said calcium silicate hydrate matrix.
 13. A methodfor producing a calcium silicate type insulating material as in claim10, wherein the amount of said pressure utilized and the duration ofsaid time employed in the curing step (b) result in a predominantlyxonotlite phase of said calcium silicate hydrate matrix.
 14. A methodfor producing a calcium silicate type insulating material as in claim12, further comprising the step of heat treating said shape to above 500degrees Fahrenheit.
 15. A method for producing a calcium silicate typeinsulating material, including the steps of: a. combining an aqueousslurry from a mixture comprising: 12 to 40 weight percent lime, 12 to 40weight percent siliceous component, up to 70 weight percent aluminasilica microspheres, 0 to 70 weight percent wollastonite, and 0 to 10weight percent organic fiber; b. reacting said aqueous slurry in anatmosphere of steam at sufficiently elevated pressure for sufficienttime to cause the lime, siliceous component, and water to form a calciumsilicate hydrate matrix; c. molding said slurry into a shape; d. dryingsaid shape to remove excess water.
 16. A method for producing a calciumsilicate type insulating material as in claim 15, wherein the amount ofsaid pressure utilized and the duration of said time employed in thereacting step (b) result in a predominantly xonotlite phase of saidcalcium silicate hydrate matrix.
 17. A method for producing a calciumsilicate type insulating material as in claim 15, wherein the amount ofsaid lime of said mixture is 14 to 20 weight percent, the amount of saidsiliceous component of said mixture is 14 to 20 weight percent, theamount of said alumina silica microspheres of said mixture is 10 to 30weight percent, the amount of said wollastonite of said mixture is 30 to50 weight percent, and the amount of said organic fiber of said mixtureis 4 to 8 weight percent.
 18. A method for producing a calcium silicatetype insulating material as in claim 17, wherein the amount of saidpressure utilized and the duration of said time employed in the reactingstep (b) result in a predominantly xonotlite phase of said calciumsilicate hydrate matrix.